PhD Thesis - Cranfield University

Chapter 5
An important difference with the power management policy is that power split decisions are
made using only power fluctuations at the DC Bus rather than the conventional methods of
monitoring the throttle input (driver input). This leads to the ability of including propulsion
as well as non-propulsion loads in the implementation framework without changing the
formulation of the policy.
5.9 Implementation of an EMS Strategy
Consider a strategy to maintain the kinetic to electrical energy balance correlation (5-28) by
regulating the SoC of the ultracapacitor bank as a function of the vehicle velocity
E uc kin
+ E = K
(5-28)
with constraints that battery and ultracapacitor SoC ranges between
SoC ≤ SoC ( k ) ≤ SoC (max)
(5-29)
batt , uc (min) batt , uc
batt , uc
where E uc is the instantaneous energy of the ultracapacitor bank and E kin is the instantaneous
kinetic energy of the vehicle, with both the energy levels balanced by constant K.
The strategy is to ensure that the ultracapacitors are held at an acceptable state of charge
such that the ultracapacitors are both capable of delivering peak power requests and are
receptive to regenerative power conditions. Since no prior information regarding the mission
profile is known, the energy balance strategy can be assumed as a speculation of energy
usage under uncertainty. As the strategy implemenation tool, fuzzy logic control is
employed. The fuzzy logic controller operating within the EMS follows a repetitive cycle that
can be described as follows. Measured variables and derived parameters are mapped into
fuzzy sets through a fuzzification process, which also capture the uncertainties of the
measured values. Following this, a fuzzy inference engine evaluates the fuzzy sets according
to control rules defined in a fuzzy logic rule-base. Based upon rule-base evaluation, an
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